92 THE NUTEITIVE FUNCTIONS. 



more or less dilated in its course through the body. At 

 the upper portion of this canal there is an opening called 

 the mouth, which is provided with an appropriate arrange- 

 ment of teeth for cutting and crushing the food, and of 

 salivary glands for affecting its lubrication. 



The food having been prepared and lubricated in this 

 manner, descends into the stomach through the oesophagus 

 (1,) by the left or cardiac opening where it is acted 

 on by the gastric juice secreted by the walls of the sto- 

 mach (3.) This fluid,' which is of an acid nature, re-acts 

 on the alimentary mass, penetrates, softens, and ultimately 

 changes it into a semi-fluid, homogeneous, and pulpy sub- 

 stance, named chyme. At the commencement of this ope- 

 ration, the communication between the stomach and intes- 

 tines is entirely closed by a valve, called the pylorus (5.) 

 As the solution advances, the dissolved parts are gradually 

 moved by the muscular contractions of the walls of the 

 stomach to its right or pyloric extremity (4.) The valve 

 called the pylorus is a very faithful sentinel. This is indi- 

 cated by its name, which is derived from two Greek words, 

 and signifies literally, to guard the gate. It will not ordi- 

 narily permit any undigested food io pass it. The quan- 

 tity of chyme, or digested food, which passes through the 

 pylorus, is at first small, but as the process of chymifica- 

 tion or digestion goes on, the flow increases, and towards 

 its termination, the chyme passes quite rapidly through 

 the valve. In the duodenum, which commences the small 

 intestine, the chyme is acted upon by the fluids secreted by 

 the liver and pancreas, that is to say, by the bile and pan- 

 creatic fluids, which are poured into the upper part of 

 the small intestines by means of a duct (6,) communica- 

 ting with these organs. These fluids, which are of an alka- 

 line nature, probably arrest the movement of dissolution 



